Tailoring electromagnetic responses in a coupled-grating system with combined modulation of near-field and far-field couplings

Herein, we establish a hybrid coupling model (HCM) containing both near- and far-field couplings to describe the electromagnetic response of the coupled-grating system composed of two parallelly aligned subwavelength dielectric gratings. The HCM shows that the near-field coupling strength only contributes to the frequency splitting of two resonant modes, while the far-field one contributes to the frequency splitting and the linewidths of two resonant modes simultaneously. By changing the distance between two dielectric gratings, both the near- and far-field coupling strengths can be flexibly tuned, giving rise to rich electromagnetic responses. In addition, the formation of Fabry-Perot bound states in the continuum in coupled-grating systems can be clearly explained by the HCM. In this paper, we not only provide an all-dielectric platform for simultaneously manipulating near- and far-field couplings but also offer a viable approach to achieve reflectance/transmittance spectra with diverse shapes.